The invention relates to microorganisms which are capable of producing an S-.alpha.-imino carboxylic acid of the general formula ##STR3## where A together with --NH-- and --CH-- is an optionally substituted 5- or 6-membered saturated heterocyclic ring.
S-.alpha.-imino carboxylic acids of Formula II, e.g., S-.alpha.-pipecolic acid are important intermediates for the preparation of numerous bioactive compounds, e.g., thioridazine or pipradol (Ng-Youn-Chen et al., J. Org. Chem., Vol. 59, No. 8, 1994).
In addition to numerous chemical racemate resolutions of (RS)-pipecolic acid and its derivatives, biotechnological racemate resolutions are also known. For example, Huh et al., Biosci., Biotech. Biochem., 56(12), 2081-2082 describe the racemate resolution of (RS)-pipecolic acid using an R-amino-acid oxidase. This entails specific oxidation of the R-isomer to .increment..sup.1 -piperideine-2-carboxylic acid, resulting in S-pipecolic acid. After chemical reduction of the .increment..sup.1 -piperideine-2-carboxylic acid to (RS)-pipecolic acid, the action of the R-amino-acid oxidase again results in S-pipecolic acid. This involves a continual decrease in the content of R-pipecolic acid. An analogous process for preparing S-proline is described in J. Ferm. Bioeng., 74, 189-190, 1992. However, these two processes have the disadvantage of not being practicable on a commercial scale. Another disadvantage is in that purified R-amino-acid oxidase must be used.
It is known further that racemic pipecolic esters are converted under the action of a lipase from Aspergillus niger into S-pipecolic acid and R-pipecolic esters (Ng-Youn-Chen et al., 1994, ibid.). However, this process has the disadvantage of S-pipecolic acid being obtained with an enantiomeric purity of only ee=93%.